It is an English acronym, short for "Sorry Mate, I Didn't See You!", a common excuse used when pedestrians get hit, doors get opened, and "accidents" happen. In the UK there is a campaign to change attitudes of the public, police practices and prosecution in the courts, saying that it is just an excuse for covering up carelessness. I personally got Smidsied in Florida as a pedestrian by a truck doing a left turn in the only intersection of a very small town; he didn't think people actually walk in the evening. I got it again the other day on my bike. Now Cyclelicious looks at SMIDSY law in the US.
Cyclelicious points us to the Chicago Bicycle Advocate, who writes:
Motorists need to get something straight: I didn't see Mr. or Ms. bicyclist, is not a defense. It is an indictment.
There is even legal precedent going back 45 years:
"It is well settled that one may not look with an unseeing eye and be absolved of the charge of negligence by asserting that he maintained a continuous lookout, yet failed to see that which he clearly should have seen."
We need to bring this British SMIDSY Campaign to North America. The four lamest words in the English language have to be "It was an accident."